Polyamines are already known as intermedite products for lightfast and weather resistant polyurethane lacquers, for example, hexamethylene diamine, 3-aminomethyl-3,5,5-trimethylcyclohexaylamine and 4,4'-diaminodicyclohexyl methane have achieved a position of great commercial importance as starting materials. The diisocyanates produced from these diamines, however, have serious disadvantages if used for the manufacture of two-component polyurethane lacquers. Thus, they have a low functionality of only 2, which means that two-component polyurethane lacquers would require longer curing times than are conventionally used in practice. In addition, they have the very serious disadvantage of a high vapor pressure which considerably reduces their usefulness as two-component reaction lacquers since they constitute a health hazard. In practice, this has prevented pure diisocyanates from acquiring any importance as lacquer polyisocyanates and instead reaction products of these diisocyanates still containing free isocyanate groups are used as hardener components.
Known reaction products of this kind include the reaction products of diisocyanates with polyalcohols such as trimethylolpropane. Polyisocyanates with biuret groups obtained as reaction products of diisocyanates (e.g. hexamethylene diisocyanate) with water have also achieved considerable commercial importance.
Compared with the diisocyanates mentioned above, these reaction products have important advantages as reactants in two-component polyurethane lacquers. For example, their functionality is higher than two and they have a low vapor pressure and are therefore physiologically harmless. However, the adduct formation also gives rise to disadvantages. The viscosity of these adducts is several times higher than that of the monomeric diisocyanate, the proportion of isocyanate reactive groups in the adducts is reduced to less than half and the preparation of these products requires expensive production processes such as thin layer distillation or extraction to isolate the monomeric diisocyanates.
Modern commercial application of these products is to some extent made difficult by these disadvantages. In view of the regulations for environmental protection and in order to save raw materials (solvents) and energy, the consumer of polyurethane lacquers seek as far as possible to use little or no solvent in his processes and, therefore, attaches considerable importance to low viscosity binders. For application of low solvent lacquers in conventional low pressure spray plants, a pigmented lacquer binder must have a viscosity of from 190 to 240 cP at room temperature. All physiologically harmless aliphatic polyisocyanates hitherto known have viscosities above this range and must be diluted with solvents.
There is, therefore, a demand for a polyamine capable of being converted into a polyisocyanate which does not have these disadvantages.
It was, therefore, an object of the present invention to provide polyamines having more than two amino groups in the molecule and a process for their preparation. It was required that these amines should react with phosgene to form odorless polyisocyanates which were liquid at room temperature and could be converted into physiologically harmless polyurethane lacquers.
This problem is solved by the synthesis of new cycloaliphatic triamines described below.